Hybrid compressor for an air-conditioning circuit

ABSTRACT

The invention relates to a hybrid compressor ( 10 ) for an air-conditioning circuit of a motor vehicle having a heat engine, said hybrid compressor being suitable for being driven, on the one hand, by said heat engine and, on the other hand, by an electric motor ( 20 ) during phases in which the drive from the heat engine is interrupted. According to the invention, said hybrid compressor ( 10 ) consists of a compression chamber ( 101 ) with variable displacement, said displacement being variable in a (variation range having an upper displacement interval in which the compression chamber ( 101 ) is driven by the heat engine, and a lower displacement interval in which the compression chamber ( 101 ) is driven by the electric motor ( 20). The invention can be used for motor vehicles having a heat engine and provided with an automatic stopping and restarting system.

The present invention relates to a hybrid compressor for anair-conditioning circuit of an engined motor vehicle.

The invention finds a particularly advantageous application in the fieldof the air-conditioning of engined motor vehicles equipped with anautomatic stopping and restarting system, such as the systems able toimplement the function known by the term “Stop and Start”,

The “Stop and Start” function consists, under certain conditions, inautomatically causing the complete stopping of the engine when thevehicle itself has stopped, and then in automatically restarting theengine following, for example, an action of the driver interpreted as arestart request.

A typical situation for implementing the “Stop and Start” function isthat of stopping at a red light. When the vehicle stops at the light,the “Stop” mode of the “Stop and Start” function causes the automaticstopping of the engine, and the vehicle then enters the “Start” modewhich allows the engine to restart automatically without it beingnecessary to use the means for initial starting of the motor, such as acontact key for example. When the light turns green, the “Start” modeautomatically restarts the motor, especially by means of analternator-starter, following the detection by the command system uponthe starting of the vehicle of the depression by the driver of theclutch pedal, of the accelerator pedal, or else of any other action thatcan be interpreted as the driver's desire to restart his vehicle. Thebenefit of the “Stop and Start” function is understood in terms ofenergy saving and pollution reduction, particularly in urbansurroundings.

Moreover, it is known that an air-conditioning circuit of an enginedvehicle comprises a refrigerant fluid compressor which is driven by theshaft of the crankshaft of the engine by way of a belt and a pulleylinked mechanically to the rod of the compressor. Stated otherwise, theair-conditioning circuit of the vehicle can only operate if the engineis running. Consequently, during the vehicle stopping phases in thecontext of the “Stop and Start” function, the air-conditioning does notoperate. It follows from this that in the course of these stoppingphases the setpoint temperature inside the cabin may not be maintained,hence a feeling of discomfort felt by the passengers of the vehicle.

To ensure maintenance of the temperature in the cabin during the enginestopping phases, it is proposed to replace the usual compressor drivenby the engine of the vehicle by a hybrid compressor consisting of twoseparate compression chambers, constituting, on the one hand, aso-called mechanical compressor whose rod is driven by the engine in thesame manner as the usual compressor and, on the other hand, a so-calledelectric compressor whose rod is driven by an auxiliary electric motor.The rods of two compression chambers are independent.

When the engine is running, outside of the stopping phases induced bythe “Stop and Start” function, the refrigerant fluid circulates in theair-conditioning circuit through the mechanical compressor driven by theshaft of the crankshaft of the motor, while the electric compressor isturned off. Conversely, during the stopping phases of the “Stop andStart” function, the refrigerant fluid is directed toward the electriccompressor, which is then driven by the electric motor. Thus, by virtueof the electric compressor, the continuity of operation of theair-conditioning circuit and the maintaining of the comfort temperaturein the cabin are carried out when the engine has stopped.

However, hybrid compressors of this type exhibit the drawback of beingvoluminous and therefore difficult to integrate. Moreover, they requirea system of complex valves which is intended to manage the communicationof the refrigerant fluid between the two compression chambers whenswitching from one compressor to the other.

Hence, an aim of the invention is to propose a hybrid compressor for anair-conditioning circuit of an engined motor vehicle, said hybridcompressor being able to be driven, on the one hand, by said engine,and, on the other hand, by an electric motor during phases ofinterruption of driving by the engine, which would be much more compact,easier to integrate and simpler to use when switching over from onedrive mode, thermal or electrical, to the other.

This aim is achieved, in accordance with the invention, because saidhybrid compressor consists of a compression chamber with variablecapacity, said capacity being variable in a span of variation exhibitinga higher interval of capacities, in which the compression chamber isdriven by the engine, and a lower interval of capacities, in which thecompression chamber is driven by the electric motor.

Thus, the hybrid compressor according to the invention comprises only asingle compression chamber instead of two for the hybrid compressor ofthe prior art described above. It is therefore much less voluminous andtherefore easier to integrate. Moreover, there is no need to provide asystem of complex valves for the passage of the refrigerant fluid fromone chamber to another during changes of drive mode, since, in theinvention, the compression chamber is single and comprises only oneintake orifice and one exit orifice for the refrigerant fluid.

Preferably, said higher and lower intervals of capacities are distinct.

Under normal operating conditions of the air-conditioning circuit, thecapacity of the compression chamber is chosen in the higher interval,the driving of the rod of the compressor being ensured by the engine.

On the other hand, during the phases of interruption of driving by theengine, especially the engine stopping phases imposed by the “Stop andStart” function, the cabin is in general already conditioned to comfortconditions, so that the refrigerative power to be provided by theelectric motor in order to maintain these conditions for a durationlimited to a few tens of seconds is markedly lower, at least by a factorof 2 to 3, than the power that must be provided by the engine. If thensuffices to reduce the capacity of the compression chamber to a valuelying in the lower interval and to turn on the electric motor until theengine is restarted by the “Stop and Start” function.

In a preferred embodiment, said compression chamber with variablecapacity is a compression chamber with rotary drive. By way of example,said compression chamber is a compression chamber with vanes withadjustable intake volume.

Advantageously, the invention provides that the driving of thecompression chamber by the engine can be disengaged from the engine forcapacities lying in said lower interval of capacities. The electricmotor is then decoupled from the engine and can ensure the driving ofthe compression rod under low power because the compression chamber thenoperates with a reduced capacity.

It was seen above that said phases of interruption of driving by theengine may be engine stopping phases, and in particular that said enginestopping phases are the stopping phases of a system for automaticstopping and restarting of the engine, such as the “Stop and Start”system.

However, the electric motor of the hybrid compressor according to theinvention may be harnessed in other circumstances, especially when saidphases of interruption of driving by the engine are vehicle accelerationphases. It is indeed known that when a vehicle accelerates theair-conditioning circuit is stopped by mechanically decoupling thecompressor from the engine, doing so in order to eliminate the resistivetorque imposed on the shaft of the crankshaft by the compressor. Underthese conditions, the air-conditioning can nonetheless be maintained bysetting into operation the electric motor of the hybrid compressor inaccordance with the invention.

In order to facilitate the turning on of the electric motor during thephases of interruption of driving by the engine, provision is made forthe hybrid compressor according to the invention to comprise means forsetting the electric motor into operation before the commencement of anengine stopping phase. The electric motor is therefore set intooperation by anticipation, before the engine actually stops. Theelectric motor, which, as is known, may be of reduced power, does nottherefore have to overcome the diverse variations in refrigerant fluidpressure which generally appear in the air-conditioning circuitfollowing the complete stopping of the air-conditioning circuit.

In practice, said means for setting the electric motor into operationare means for detecting stopping of the engine of a system for automaticstopping and restarting of the engine. Within the framework of the “Stopand Start” function, these detection means may be extremely varied andgenerally depend on the strategy chosen by the constructors. It ispossible to cite for example the detection of an action on the brakepedal when the speed of the vehicle goes below a given threshold.

Finally, the invention also relates to an assembly of a hybridcompressor according to the invention and of an electric motor fordriving said hybrid compressor, in which the electric motor is suppliedby a low-voltage direct current. More specially, said low-voltage directcurrent is provided by the 12 V network of the vehicle. Theimplementation of the hybrid compressor in accordance with the inventionis then greatly simplified since it does not involve any modification ofthe onboard electrical network.

The description which follows with regard to the appended drawings,which are given by way of nonlimiting examples, will elucidate theinvention and the manner in which it may be embodied.

FIG. 1 is a diagram of an air-conditioning circuit comprising a hybridcompressor in accordance with the invention.

FIG. 2 is a chart illustrating the operation of the hybrid compressor ofFIG. 1 for various life situations of a motor vehicle equipped with the“Stop and Start” function.

FIG. 3 is a block diagram of a control circuit of the electric motor fordriving the hybrid compressor of FIG. 1.

In FIG. 1 is represented a conventional air-conditioning circuit of anengined motor vehicle, comprising a compressor 10 of a refrigerant fluidwhich may be an organic, inorganic or eutectic fluid. It is possible tocite as nonlimiting examples supercritical carbon dioxide CO₂, therefrigerants known by the references R134A, 1234yf or else GAR (“GlobalAlternative Refrigerant”). Downstream of the compressor 10, thepressurized refrigerant fluid passes through a heat exchanger 11 calleda “gas cooler” for carbon dioxide or a “condenser” for R134A since, inthis case, the refrigerant initially in the gas phase exits thecondenser in liquid form.

In the example of FIG. 1, the exchanger 11 may be a water-typeexchanger, or an air-type exchanger cooled directly by the outside air.

The refrigerant fluid is thereafter conducted toward a relief valve 12so that it is cooled before entering the evaporator 13 where heatexchange then occurs between the cooled refrigerant and air blown towardthe cabin of the vehicle.

The refrigerant fluid, reheated on exit from the evaporator 13, is thenreturned to the compressor 10 to perform a new thermal cycle.

As may be seen in FIG. 1, the compressor 10 of FIG. 1 is a hybridcompressor comprising a compression chamber 101 with variable capacitywhose rod 102 may be driven, either by an electric motor 20, or by theshaft of the crankshaft of the engine (not represented) of the vehiclevia a belt and a pulley 30 able to be linked mechanically to the rod 102by way of a clutch 31.

During nominal operation, the rod 102 of the compression chamber 101 isdriven by the engine, the pulley 30 being coupled to the rod 102 by theclutch 31. The capacity of the compression chamber is then chosen in ahigher interval of values close to the maximum capacity, from 90 to 110cm³ for example. Under these conditions, the hybrid compressor 10 iscapable of ensuring an optimal comfort level inside the cabin of thevehicle, whatever the outside temperature, the sunshine and the degreeof relative humidity.

However, it can happen, in certain circumstances, that theair-conditioning compressor is no longer driven by the engine of thevehicle and that, consequently, the air-conditioning circuit ceases tooperate and no longer ensures maintenance of the comfort temperatureinside the cabin. Such is the case especially during the engine stoppingphases imposed by a system for automatic stopping and restarting of theengine able to implement the “Stop and Start” function of vehiclesequipped with this function.

In order to ensure continuity of air-conditioning, the electric motor 20is set into operation during these stopping phases so as to maintain thecirculation of the refrigerant fluid in the air-conditioning circuit.Stated otherwise, it may be considered that the electric motor thensubstitutes itself for the engine. Of course, the latter is, preferably,disengaged from the compression rod 102.

The block diagram of FIG. 3 shows how the switchover of the driving ofthe compressor 10 from the engine to the electric motor 20 is performedin practice.

When it receives an engine stop cue STOP from the automatic stopping andrestarting system, the electronic control unit 50 of theair-conditioning circuit transmits a signal for engaging the electricmotor 20 to a power module 51. In response to this signal, the module 51actuates an auxiliary electric motor 103 making it possible to modifythe capacity of the compression chamber 101 from the value of the higherinterval where it was before the interruption of the driving by theengine to a value of the lower interval, between 20 and 40 cm³ forexample. Next, after decoupling of the pulley 30 by the clutch 31, thepower module 51 dispatches to the electric motor 20 the power necessaryto maintain, during the engine stopping phase, the operation of thecompressor 10 at a sufficient level, having regard to the initialair-conditioning conditions before the stopping of the engine.

Indeed, at the moment at which the electric motor 20 takes over from theengine upon stoppage, the cabin of the vehicle is in principle alreadyat the comfort temperature, so that, having regard to the fact that theduration of the stopping phases is generally limited to a few tens ofseconds, the refrigerative power to be provided by the electric motor 20is relatively low. By way of example, in a conventional manner, arefrigerative power of 6 kW is necessary in order to guarantee comfortin the cabin of a vehicle exposed to a high temperature of 25 to 45° C.under sunshine of 1000 W.m² and a relative humidity of 50 and 60%.However, when the vehicle is already conditioned to the comforttemperature, the refrigerative power to be provided lies between 1 kWand 3 kW depending on the segment of the vehicle. An electrical power ofthe order of 500 to 800 W to be provided by the power module 51 is thensufficient to maintain comfort in the cabin.

Consequently, the capacity of the compression chamber 101 may bereduced, with respect to the nominal operating conditions, to valueslying in a lower interval of capacities of about the minimum capacity,from 20 to 40 cm³ for example, distinct from the higher interval definedabove.

Of course, the higher and lower intervals of capacities may be simplyreduced to the maximum and minimum capacities alone. The compressionchamber 101 then switches in a binary manner between these twocapacities depending on whether the motive drive for the rod of thechamber is the engine or the electric motor.

Having regard to the fact that the power requested of the electric motoris relatively low, it is possible to envisage the use of an electricmotor, with or without brushes, supplied by a low-voltage direct currentprovided, in particular, by the 12 V network of the vehicle, it beingpossible for the electric current source to be a battery 40 or an extraunit furnished or not with a storage capacitor.

In a practical manner, the compression chamber 101 with variablecapacity may be embodied by a compression chamber with rotary drive,especially a conventional compression chamber with vanes whose intakevolume, corresponding to the capacity, can be adjusted between theminimum value of 20 cm³, for example, and the maximum value of 110 cm³,for example, by varying the position of the intake orifice in thechamber.

In the chart of FIG. 2 have been represented the operating states of theengine and of the electric motor 20 for driving the hybrid compressor 10of a motor vehicle equipped with the “Stop and Start” function, thevalue 0 corresponding to the stopping of the motor and the value 1 toits operation.

As may be seen in this figure, when the engine is stopped by the “Stopand Start” function, the electric motor 20 is set into operation, inaccordance with the invention, so as to ensure maintenance of comfort inthe cabin during the engine stopping phase. However, it may be notedthat the setting into operation of the electric motor 20 is performedwith anticipation, that is to say before the commencement of an enginestopping phase triggered by the “Stop and Start” function.

The advantage of this setup is that the electric motor does not have toprovide the additional torque which would be necessary in order toovercome the resistive torque induced by the rearrangements ofrefrigerant fluid pressure in the air-conditioning circuit which couldoccur at the moment of the stopping of the engine. The power of theelectric motor 20 can therefore be rated accordingly.

To carry out this anticipation of the electric motor, it is possible touse the means implemented by the “Stop and Start” function to detectwhether the engine stopping conditions are satisfied and decide as tothe stopping of the engine. As soon as the “Stop and Start” functiondecides to stop the engine, the electric motor 20 is immediately setinto operation before the actual stopping of the engine. The conditionsof automatic stopping of the engine depend on the strategy adopted bythe vehicle constructor. It is possible to cite, inter alia, an actionon the brake pedal when the vehicle is traveling at low speed, less than5 km/hour for example.

FIG. 2 shows another circumstance in which the electric motor 20 may beset into operation so as to guarantee continuity of the comforttemperature during a stoppage of the air-conditioning circuit. In thiscircumstance, the stopping of the air-conditioning circuit is not due toa stopping of the engine, but to the decoupling of the drive pulley 30from the rod 102 of the compression chamber 101. This situation canoccur during acceleration of the vehicle for example, so as to apply amaximum torque to the shaft of the crankshaft and afford the bestresponse to the acceleration request.

In this case, the electric motor 20 is set into operation as soon as theengine is decoupled from the compression rod 102.

1. A hybrid compressor for an air-conditioning circuit of an enginemotor vehicle, said hybrid compressor being able to be driven by saidengine and by an electric motor during phases of interruption of drivingby the engine, the hybrid compressor comprising: a compression chamberwith variable capacity, said capacity being variable in a span ofvariation exhibiting a higher interval of capacities, in which thecompression chamber is driven by the engine, and a lower interval ofcapacities, in which the compression chamber is driven by the electricmotor.
 2. The hybrid compressor as claimed in claim 1, wherein saidhigher and lower intervals of capacities are distinct.
 3. The hybridcompressor as claimed in claim 1, wherein the driving of the compressionchamber by the engine is disengaged from the engine for capacitieswithin said lower interval of capacities.
 4. The hybrid compressor asclaimed in claim 1, wherein said compression chamber with variablecapacity is a compression chamber with rotary drive.
 5. The hybridcompressor as claimed in claim 4, wherein said compression chamber is acompression chamber with vanes with adjustable intake volume.
 6. Thehybrid compressor as claimed in claim 1, wherein said phases ofinterruption of driving by the engine are engine stopping phases.
 7. Thehybrid compressor as claimed in claim 6, wherein said engine stoppingphases are the stopping phases of a system for automatic stopping andrestarting of the engine (“Stop and Start”).
 8. The hybrid compressor asclaimed in claim 1, wherein said phases of interruption of driving bythe engine are vehicle acceleration phases.
 9. The hybrid compressor asclaimed in claim 1, further comprising means for setting the electricmotor into operation before commencement of said interruption of drivingby the engine.
 10. The hybrid compressor as claimed in claim 9, whereinsaid means for setting the electric motor into operation are means fordetecting stopping of the engine of a system for automatic stopping andrestarting of the engine (“Stop and Start”).
 11. An assembly comprisinga hybrid compressor as claimed in claim 1 and an electric motor fordriving said hybrid compressor, wherein the electric motor is suppliedby a low-voltage direct current.
 12. The assembly as claimed in claim11, wherein said low-voltage direct current is provided by the 12 Vnetwork of the vehicle.